The present invention relates generally to optical devices and, more particularly, to a microfluidic device defined by a plurality of parallel, elongate channels for containing a sample and optical apparatus for irradiating a sample in the channels and measuring absorption of the sample and diffraction of electromagnetic radiation by the system for sensor and modulation applications.
The invention described herein was supported at least in part by the Defense Advanced Research Project Agency (DARPA) and by the National Science Foundation (NSF) under award ECS-9729405. The government has certain rights in the invention.
Devices for spatial light modulation based on liquid crystals, colloidal crystal hydrogels, materials showing photochromic and photoelastic effects, and micromachined structures are known. Some of these devices operate by exploiting differences in phase or absorption of electromagnetic radiation.
Differences in phase of electromagnetic radiation can be produced by varying a path that the radiation follows, for example by passage of the radiation through media of differing refractive index. Phase differences of light have been exploited for a variety of uses including sensors, apparatus for photolithography, optical displays, optical communication, fiber optic carriers, and the like.
Absorption of material by electromagnetic radiation is determied routinely. Absorption of light by fluid samples typically is determined by measuring absorption of light through an empty sample chamber, then measuring absorption of the same light through the same chamber filled with a sample, and comparing the two. A source of electromagnetic radiation is positioned on a first side of the chamber and a detector is positioned on the opposite side to detect radiation passing through the chamber, both filled and unfilled. These procedures are carried out with so-called absorption spectrometers which can determine absorption of a sample over a range of electromagnetic radiation frequencies.
Solgaard, et al., in xe2x80x9cDeformable Grating Optical Modulatorxe2x80x9d, Optics Letters 17, 9 (1992) describe a deformable light grating modulator based on electrically controlling the amplitude of a micromachined phase grating. The described structure includes silicon nitride beams suspended above a substrate. With no voltage applied between the substrate and the individual beams, the total path length difference for light reflected from the beams and from the substrate equals the wavelength of the incoming light. Reflections from the beams and from the substrate add in phase, and the grating reflects the light as a flat mirror. When a voltage is applied between the beams and the substrate, electrostatic force pulls the beams down. The total path length difference for the light reflected from the beams and from the substrate is now xc2xd of the wavelength, and the reflections interfere destructively, causing light to be diffracted. Solgaard, et al., state that ease of integration is expected to make deformable mirror modulators strong competitors with liquid crystal and electro-optic spacial light modulators in display technologies and for optical signal processing.
Delamarche, et al., xe2x80x9cMicrofluidic Networks for Chemical Patterning of Substrates: Design and Application to Bioassays,xe2x80x9d J. Am. Chem. Soc., 1998, 120, 500-508, describe a microfluidic network useful for the small-scale patterned delivery of reactants to surfaces using the elastomer poly(dimethylsiloxane) as at least a portion of the channels. Woolley, et al., in xe2x80x9cHigh-Speed DNA Genotyping Using Microfabricated Capillary Array Electrophoresis Chips,xe2x80x9d Analytical Chemistry, 69:11, Jun. 1, 1997, describe flowing a fluid through multiple channels and measuring optical characteristics of the fluid.
As mentioned above, measurement of properties of fluid samples in sample chambers is carried out routinely. There are many uses for systems that cause fluid to flow through channels, including very small channels. In an article entitled xe2x80x9cDownsizing Chemistry,xe2x80x9d Chemical and Engineering News, Feb. 22, 1999, 27-36, a variety of systems are described for analyzing very small amounts of samples and reagents on chemical xe2x80x9cchipsxe2x80x9d that include very small fluid channels and small reaction/analysis chambers. Small-scale systems are currently being developed for genetic analysis, clinical diagnostics, drug screening, and environmental monitoring. Such small-scale systems are commonly referred to as Microscale Total Analysis Systems (see, for example, Kricka, L. J.; Wilding, P. Micromechanics and Nanotechnology, in Handbook of Clinical Automation, Robotics and Optimization, Kost, G. J., Welsh, J., Eds., John Wiley and Sons, New York, 1996, p. 45; van den Berg, A., Bergveld, P., Eds., Micro Total Analysis Systems, Kluwer Academic Publishers, London, 1995; Manz, A., Becker, H., Eds. Microsystem Technology in Chemistry and Life Sciences, Springer-Verlag, Berlin, Germany, 1998; Manz, A., Harrison, D. J., Verpoorte, E., Wildmer, H. M. Adv. Chromatogr., 1993, 33, 1; Kricka, L. J., Wilding, P. Pure Appl. Chem., 1996, 68, 1831). Microscale Total Analysis Systems must be able to handle liquid or gas samples at very small scale, and must be compatible with chip-based substrates. Microfluidics, the behavior of fluid flow in very small-scale systems, therefore is central to the development of these systems.
Miniaturized capillary electrophoresis systems are known. Capillary electrophoresis is a separation technique that, conventionally, is typically carried out in fused silica capillaries. Capillary electrophoresis within polymer channels also is known. For a discussion of miniaturized capillary electrophoresis techniques, see Duffy et al., xe2x80x9cRapid Prototyping of Microfluidic Systems in Poly(dimethylsiloxane),xe2x80x9d Analytical Chemistry, 70, 23, 4974-4984 (Dec. 1, 1998), and references therein.
Electroosmotic flow is a known technique for urging the flow of fluid within a channel by applying electric fields along the channels. Electroosmotic flow typically is carried out within glass channels in which it is relatively easy to create a negatively-charged interior channel surface to support electroosmotic flow.
Microfluidic systems based upon poly(dimethylsiloxane) are known. See Duffy, et al., referenced above, and references therein.
While the above and other reports describe in many cases useful optical modulators and sensors, and useful microfluidic systems, a need exists for simplified, inexpensive devices that can serve as effective modulators and/or can provide significant information when used as a sensor and microfluidic systems that can be used in these and other techniques. It is an object of the invention to provide such devices.
The present invention provides systems and methods for optical modulation and sensing. Some of these aspects and methods are described in the accompanying claims.
A device of the invention can be a diffraction grating defined by essentially parallel lines. But the device is not limited to a diffraction grating with evenly spaced, parallel lines. By changing the width and spacing of the microchannels more complex light patterns can be made, e.g. a variety of patterns defined by microchannels that change the spatial distribution of light passing through the device through diffraction effects, through constructive and destructive interference of light passing through different regions of the device, such as a Fresnel lens that focuses light using a planar array of channels.